Worse still, T-shirts emblazoned with Bart's life philosophy – "Underachiever and proud of it!" – undermined the very mission of the schools in which they were worn. By 1992, the president of the United States himself was framing domestic policy in terms of this dangerous TV cartoon. In January, he promised to help American families become "a lot more like the Waltons and a lot less like the Simpsons."

Instead, something extraordinary happened. "The Simpsons" hit its stride, and the writers figured out that Homer, not Bart, was the narrative fulcrum of the show. Noble Homer would suffer the slings and arrows of outrageous fortune in every episode, but, with the promise of nothing more than a doughnut, would always rise to fight another day.

By the third or fourth season, thinking adults started to see a masterpiece in the making. In 1998, when America's poet laureate(!) paid tribute to "The Simpsons" in The New York Times Magazine(!), it was clear that whoever still thought the show was nothing but toxic tomfoolery simply wasn't watching it.

By century's end, scholars, journalists, philosophers, and professors were producing academic theses, doctoral dissertations, and books analyzing and celebrating "The Simpsons." The claim that it was one of the best shows in TV history had become undisputed orthodoxy.

As for the kids, I think "The Simpsons" is good for them. Like Mad magazine did for previous generations, "The Simpsons" encouraged the development of a healthy sense of social satire, something children were going to need in an era that would also bring them O.J. Simpson, Monica Lewinsky, and "Who Wants to Marry a Multi-Millionaire?"

Between the raunchy sophistication of "The Simpsons" and the family-friendly vapidity of "Full House," I think an eight-year-old would be better off with the former.

No, it didn't teach respect for authority, but in many other ways it was very traditional. Carefully cloaked in the vestments of irony and attitude, a lot of very positive messages surreptitiously slipped into the show. (We shouldn't forget, however, that the program was also a major participant in the hyper-commercialism that it regularly burlesqued.)

Although most people now agree that "The Simpsons" is in its baroque decline (by my formula, which calculates the effective age of a TV series at a rate of dog years plus two, "The Simpsons," at 18, is actually 162), even a bad "Simpsons" is better that a good episode of most other network comedies. And if we look at the series as a whole, it stands up alongside the best of American comic art, in the same category as Charlie Chaplin and Buster Keaton, "Krazy Kat," "The Far Side," Sid Caesar, and Ernie Kovacs.

The show's remarkable endurance is based on a foundation of fine writing. Far from a band of itinerant hacks, the writing staff of "The Simpsons" has included more than 20 Harvard alumni. Alongside the dizzying number of popular culture references are obscure literary allusions that could only have come from the reading list of a swanky liberal arts institution.

Animation also aided its longevity (Bart, were he human, would now be 28), and one of the important legacies left by "The Simpsons" was that it liberated TV animation from the confines of Saturday morning. "The Flintstones" had been billed as an adult cartoon and it aired in prime time, but it was always just a kid's show.

"The Simpsons" took the TV cartoon away from superheroes, talking animals, and stone-age families, and cleared the way for the flowering of a new genre that would soon include "Beavis and Butt-head," "Dr. Katz: Professional Therapist," "King of the Hill," "Family Guy," and "South Park," not to mention the Adult Swim line-up on Cartoon Network.

The greatest legacy of "The Simpsons," though, will ultimately be itself. It is the most rerunable show of all time. With so many episodes already in the can, it can now play five days a week for over a year and a half without a repeat. And there's always something new to notice in every episode – the older you get, the more you see. The clothes and hairdos will never be out of style because they were never in style in the first place.

Whether the "Simpsons" movie, which opens Fri-day, is a hit or a flop doesn't matter. In the end, it will be a DVD bonus feature attached to that which really counts: the 400-plus episodes that make up one of the best, and longest, comedies in any medium.

• Robert Thompson is a professor at Syracuse University's S.I. Newhouse School of Public Communications, where he also is director of the Bleier Center for Television and Popular Culture.